Mechanisms of Hearing Loss after Cochlear Implantation

Oregon Health & Science University, Portland OR

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Abstract

Project Summary Approximately 22 million Americans have a hearing impairment. Cochlear implants (CIs), a neural prosthesis developed to treat severe hearing loss, have significantly improved speech understanding in quiet for many individuals with hearing loss. However, benefit remains highly variable across the patient population, and speech understanding in noise remains a problem. A recent advance is the Hybrid or Electro-Acoustic Stimulation (EAS) CI, which is shorter and thinner than a traditional CI, and together with soft surgery techniques enables preservation of hearing in the implanted ear. This allows combined electric and acoustic stimulation (EAS) in the same ear, which dramatically improves speech perception in noise, voice recognition, and musical melody and timbre recognition. However, currently 30-55% of EAS CI recipients lose more than 30 dB of hearing after implantation, which can negate these benefits. Thus, post-surgical hearing preservation rates need to be improved to improve outcomes for EAS CIs. In order to improve hearing preservation, we need to understand the mechanisms of post-implantation hearing loss. Our preliminary studies indicate one likely mechanism of hearing loss: surgical trauma may reduce the blood supply to the lateral wall of the cochlea essential for maintaining the endocochlear potential necessary for hearing. Alternatively, inflammation in response to the surgery or the presence of the electrode may decrease ion homeostasis or compromise the integrity of the blood-labyrinth barrier in the lateral wall which are both necessary for maintaining the endocochlear potential. In this proposal, we will examine the role of endocochlear potential loss and lateral wall changes in hearing loss. The long-term goal of this research program is to investigate how cochlear implantation affects hearing. The findings will be highly clinically significant for building a mechanism-based framework for the design of future treatments and strategies to reduce hearing loss and improve outcomes with cochlear implants.